Metalloboranes as fogging agents in direct positive emulsions

ABSTRACT

Direct-positive photographic elements having good sensitometric characteristics and aging stability are prepared by incorporating in the silver halide emulsion from 10 8 to 10 4 mole per 1.5 moles of silver nitrate of at least one metalloborane as a chemical fogging agent selected from the group containing the metals, platinum, nickel, cobalt, rhenium, iron or silver in its structure.

United States Patent [191 Bigelow Apr. 16, 1974 METALLOBORANES AS FOGGING AGENTS IN DIRECT POSITIVE EMULSIONS [75] Inventor: John Bigelow, Rochester, NY.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Feb. 15, 1972 [21] Appl. No.: 226,549

[52] US. Cl. 96/108 [51] Int. Cl, 603C 1/28 [58] Field of Search 96/108, 64

[56] References Cited UNITED STATES PATENTS 3,655,390 4/1972 Overman 96/108 Wark 96/108 Bigelow et al, 96/64 Primary Examiner-Norman G. Torchin Assistant Examiner--Won H. Louie, Jr.

[ 5 7] ABSTRACT 11 Claims, No Drawings METALLOBORANES AS FOGGING AGENTS IN DIRECT POSITIVE EMULSIONS BACKGROUND OF THE INVENTION 1. Field of Invention This invention is directed to direct positive colloid silver halide emulsions. More particularly it relates to such emulsions which are prefogged by a chemical fogging agent. Still more particularly this invention relates to direct positive photographic elements comprising a light-sensitive layer coated from such emulsion. In a more particular aspect of the invention, it relates to chemically fogging direct positive emulsions with metalloborane compounds taken from the group consisting of metalloboranes, metallothiaboranes and metallocarboranes. The metalloboranes are borane compounds with metals in which some of the metal atom orbitals (i.e., electron orbits) participate in the icosohedral or other bonding framework. 1

2. Description of the Prior Art Direct positive emulsions and elements coated therewith are, of course, well known and there are many different methods of producing direct positive images. For example, a silver halide emulsion layer may be given a short overall exposure of high intensity radiation and then given a longer imagewise exposure of lower intensity. Upon development, a direct positive will be obtained. Another method is to expose imagewise and develop and bleach out developed silver and then flash expose and redevelop. A still further method is to use emulsion coated elements, the emulsions of which have been chemically fogged with, for example, formaldehyde, hydrazine, sodium arsenite, silver ions and other nonsulfide fogging agents thus eliminating a solarizing exposure or a bleach out step and redevelopment. Upon imagewise exposure and redevelopment of such chemically fogged elements,'a positive image is obtained. In direct positive elements utilizing this latter method there is usually incorporated a desensitizing compound, usually a desensitizing dye. A significant improvement was made in the art by the use of amine boranes as chemical fogging agents in direct positive emulsion systems. Elements comprising such emulsions are described and claimed in Assignees Bigelow and Burt, U.S. Pat. No. 3,361,564; Burt, U.S. Pat. No. 3,445,235 and Assignees Overman, U.S. Pat. No. 3,655,390. The Burt patent discloses and claims the use of rhodium and iridium salts in direct positive emulsions described in the above Bigelow and Burt patent and the Overman application discloses the use of bismuth salts as antikink agents. The emulsion coated elements of the above patents are quite fast as compared to direct positive elements of the prior art and avoid many of the disadvantages of long exposure times, low reversal densities, undesirable stain due to desensitizing dyes, as well as undesirable contrast, and a multiplicity of exposure steps and processing operations. Improvements in speed and other sensitometric properties of the above patents are taught by Assignees Burt, U.S. Pat. No. 3,607,288 issued on Sept. 21, 1971 and Assignees Burt and Ciavarri, U.S. Pat. No. 3,647,455 issued on Mar. 7, 1 9 72.

The use of a new class .of cyclic cage type borane compounds comprising a cage type skeletal framework or a fragment thereof as. chemical fogging agents in direct positive emulsion having certain advantages of improved shelf life or aging stability and contrast are de SUMMARY OF THE INVENTION It has now been found that the advantages noted in the use of boranes described in the above patents as chemical foggers for direct positive emulsions can be retained by the use of metalloboranes with the added advantage that the compounds have high thermal stability and appear to have moderate resistance to hydrolytic and oxidative degradation thus making them more convenient to use in manufacturing operations. The new metalloborane compounds are selected from the group consisting of metalloboranes, metallothiaboranes and metallocarboranes in which the metal atom orbitals participate in an icosahedral or other bonding framework and are derived from polyhydral or other boranes. They may be added to the emulsions in amounts ranging from 10 mole to 10* mole per 1.5 moles of silver nitrate. They may be added to the emulsion as a solution with a suitable solvent, i.e., water, ethyl alcohol, benzene, acetone, dioxane, etc.'Dimethyl sulfoxide may also be used for some of the metalloboranes.

Some of the metalloboranes are more effective than others as chemical fogging agents in direct positive silver halide emulsions. Also the effectiveness of some metalloboranes in fogging the silver halide emulsions is not affected by the pH of the system and they show good fogging properties under acid as well as alkaline conditions. It is important, however, that the metalloborane compounds be added at the beginning, during or before the end of the digestion period after the excess salts resulting from the precipitation of silver halides have been removed by washing. The pH of the emulsion is generally adjusted to 9.0 or below. The fogging effect of the metalloboranes is bleachable by light prior to development.

The emulsions of the invention may also contain a rhodium or iridium salt in an amount of from 1.5 to 325 mgm per mole of silver as described in Assignees Burt U.S. Pat. No. 3,361,564. 1

Suitable developers are conventional, alkaline, photographic developingsolutions useful for standard direct positive emulsions in the absence of the novel fogging agents and their combination with other ingredients. While the silver halide systerrrused in this invention is generally silver chlorobromide, other types, e.g., silver chloride, silver iodobromide, silver iodochloride and silver iodobromochloride may be used with the metalloborane compounds.

Among the metalloboranes which have been found useful as chemical fogging agents in this invention are the metalloboranes, metallothiaboranes and the metallocarboranes, representative examples of which are shown in the following list.

COMPOUND FORMULA HP yDa h g n u The general method of preparation of these metalloboranes is described in Polyhedral Boranes by Earl L. Muetterties and Walter H. Knoth, published by Marcel Dekker, Inc. New York and related bibliographicreferences made of record in that publication.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For most efficient fogging action it is preferred that the metalloborane compounds be added to the silver halide emulsion after it has been made, ripened and washed to remove excess soluble salts resulting from the formation of the silver halides. Conveniently, the

metalloborane compounds are added just prior to or during the digestion or after-ripening period. The pH of the emulsion is adjusted between 3.0 and 9.0 and preferably between 3.0 and 7.0 and maintained at a preselected level in this range during the digestion period. After digestion, the pH is adjusted to the desired coating pH and the conventional coating aids are added. Coating aids such as saponin, sodium salts of polyether sulfonates, alkyl sulfonates, cetyl betaine etc. can be utilized. The emulsion is then coated and dried in a manner well known to those skilled in the manufacture of photographic silver halide emulsion coated elements.

The sensitometric characteristics of the directpositive emulsions may be determined by exposing strips of elements coated with the emulsions in an intensity scale sensitometer (described on page 616, Mees, The Theory of the Photographic Process, Macmillan Company, New York 1942) using a suitable step wedge and light intensity depending upon the inherent speed of the emulsion. Direct positives are, of course, tailored to meet certain needs in the industry and are manufactured accordingly. After exposure in the sensitometer, the strips are developed in suitable developers as shown below, immersed in a shortstop bath and fixed in a conventional fixer, washed and dried.

In evaluation of the processed strips, the toe of the characteristic curve is equal to the number of steps between density 0.25 and density 0.01. Maximum density (D is the highest density value obtained on the image of the step wedge. The speed of a typical low speed commercial direct positive in terms of 100/E X is about 103 and the conventional material has a maximum density of about 3.5.

The invention will now be illustrated in and by the following examples:

EXAMPLE 1 A direct positive emulsion was made in the following manner. To acidified aqueous solution of gelatin containing 1 mole of potassium chloride and 6.9 X 10 mole of rhodium trichloride, there was rapidly added 1 1 l gelatin and the pH was adjusted to 7.0 and portions of the emulsion were heated tol30F during which the borane compound CSB H S and metalloboranes were added to the portions as indicated in the following table. The emulsions were digested for minutes at 130F. The borane compound CsB l-I S is disclosed and claimed in Assignees Bigelow U.S. Ser. No. 62,650 filed Aug. 10, 1970 and was used here as a control sample. (It is not a metalloborane but a metal salt of a thiaborane.) After digestion, the emulsion was cooled to F, the wetting agent, saponin, was added and the viscosity was suitably adjusted and the emulsion was coated on a photographic quality film support and dried in a conventional manner. The sensitometric strips were exposed in the above described sensitometer using a No. 3 lamp, SQRTZ Ser. No. 8876418 for 16 seconds. The strips were developed in the two following developers, 3 minutes in Developer 1 and 1% minutes in Developer II.

Developer 1 (High Contrast Type) Sensitometric evaluation adduced the following data:

TABLE I 4X10 mole per Strip 1.5 moles Ag No. halide Dev Speed Dmax Toe Fog Borane Compound IOO/EXIO" l [(p-tolylhP]. 1 6.0+ 1.56

g II H 2 Cs(B, ,H S),Co l1 1 6.22 3.73 3 B,,,SH, Re(CO) 11 20,000 .89 2.6 .16 4 [(C,H,),P],Pt(H) 11 110,000 .51 6.7 .06

BIOHIOS 5 [(C,H,);,P],Pt ll 6.0+ .84

s iz 6 [(C,H,),P],PtB,H l1 4.0+ .24 7 do. 1 4.0+ .23 8 2.4X10 mole/ 11 12,300 3.49 .00

1.5 mole AgHal CsB,H,, S (Control) Example 1 was repeated except that hydrochloroauric acid (HAuCh) was added to some portions and also the cesium salt of thiaborane (csfl H S) was added with the metalloborane compound as indicated in the following table.

TABLE 11 Fogging Agent Variation Mole/1.5 Moles 4 X Mole/ Strip. AgHal I 1.5 Moles AgHal.

No. HAuCl csa,n,,s Metalloborane Dev. Speed Dmax Toe Fog 1 Cs(B,,,1-1 CH ),Fe 11 0.0 0.0 2 31.7X10 12,000 5.68 1.2 0.10 3 [(p-tolylhP], n .14 .01

B n n 4 3.7.X10 do. 11 6.0+ .16 5 4x10- Cs(B, 1-1, S) Co 1 902,000 .93 5.6 .00 6 do. do. 11 80,000 3.88 6 1 .08 7 Cs (13, l1, CN1-1,) Ni 11 0.0 .00 8 37x10 do. ll .14 .00 9 (B H ocNHq)2Nl 11 0.0 .00 10 3.7X10 v 11 330,000 1.07 6.8 0.2 11 [(C,H P],PtB ,H S 11 0.0 0.0 12 3.7}(10' i do. 11 340,000 1.47 5.9 0.0 13 2.66X10" Control ll 14 3.7);10" 4X10" Control 11 754,000 .87 8.1 0.0 15 4.95X10' 2.66X10 Conlrol 11 1.37 .05

EXAMPLE 111 Example 1 was repeated using the metalloborane, Cs(B H S) Co alone and in combination with hydrochloroauric acid (HAuCL) and using the borane compound, CsB H s as a control as indicated in the following table: l

are capable of producing extremely fast direct positive elements. The elements of this invention, as shown in the examples, may be developed in any standard developing solution either of the cbntinuious tone type or the high contrast lithographic type using standard techniques. Variations in the developing solution will have TABLE III Mole/1.5 Mole Mole/1.5 mole Strip AgHal AgHal No. Cs(B H S) Co HAuCl Dev Speed Dmax Toe Fog l 4X10? 0 1 16,000 2.21 3 .06 2 do. 0 11 12,900 2.51 2.18 .08 3 4 l0"' 0 1 0.0 .00 4 do. 0 11 0.0 .00 e 5 4X10 3.72 10" I 3.01 .30 6 do. do. 11 2.83 .30 7 4X10" do. 1 69,700 2.71 5.22 .00 8 do. do. lI 72,400 2.63 5.33 .00 9 4X10 do. 1 .17 .00 10 do. do. 11 1,020,000 .49 9.0 .00 11 4X10 do. 1 0.0 .00 12 do. do. 11 0.0 .00 13 4x10" do. I .19 .00

C53, H s (control) 14 do. do. 11 947,000 .49 8.75 .00

It will be apparent that the presence of the gold compound produces an effect with an amount of metallobo-. rane which does not occur with the use of the metalloborane alone.

EXAMPLE IV Example I was repeated except that the digestion time was varied as indicated in the table and 3.72 10' mole hydrochloroauric acid per 1.5 moles of silver halide was'used with the metallo borane compounds.

TABLE IV Metalloborane Mole per Strip 1.5 Moles Dig.

No. Formulae AgHal Time Dev Speed Dmax Toe Fog 4 do. do. do. 11 2,090,000 .31 11.0 .00 5 do. 4X10- do. I .01 .00 6 do. do. do. 11 .05 .00 7 CsB,l-l S(control) do. do. I 947,000 .47 8.75 .00 8 do. do. do. 11 597,000 .71 7.36 .00 9 Cs,(B,,,H,,,CNH,),Ni 1.5)(10 2 hrs 1 102,000 2.75 5.26 .01 10 do. do. do. ll 85,000 2.58 5.78 .01 11 do. 8X10 do. I 313,000 .97 5.64 .00 12 do. do. do. 11 217,500 1.25 4.55 .00 13 do. 4X10 do. I .15 .00 14 do. do. do. 11 1,450,000 .37 10.0 .00 15 CsB,H,,S(control) do. do. 1 497,000 .92 6.9 .00 16 do. do. do. ll 271,000 1.50 5.23 .00

The silver halide emulsions of this invention can be made with any of the macromolecular, waterpermeable colloids known to be suitable for the purpose of acting as a colloid carrier for silver halide grains. In addition to gelatin, there may be used polyvinyl alcohol and its derivatives, e.g., partially polyvinyl acetates, ethers and acetals, hydrolyzed interpolymers of vinyl acetate and unsaturated addition polymerizable compounds such as maleic anhydride, acrylic and methacrylic acid esters, poly-N-vinyllactams, polysaccharides, e.g., dextran, dextrin, etc., the hydrophilic copolymers disclosed in Shacklett, U.S. Pat. No. 2,833,650, hydrophilic cellulose ethers and esters, and acrylamide polymers. Mixtures of these binders can also be used as well as water-permeable binding agents' containing dispersed polymerized vinyl compounds such as those disclosed in Nottorf, U.S. Pat. No. 3,142,568 issued July 28, 1964.

The emulsions of this invention may be coated on any suitable support including photographic quality paper and transparent film. For example, the cellulosic support, e.g., cellulose acetate, cellulose triacetate, cellulose mixed esters, etc., may be used. Polymerized vinyl compounds, e.g., copolymerized vinyl acetate and vinyl chloride, polystyrene and polymerized acrylates may also be mentioned. The film formed from the polyesters made according to the teachings of Alles, U.S. Pat. No. 2,779,684 and the patents referred to in the specification of that patent may be used. Other suitable supports are the polyethylene terephthalate/isophthalates of British Patent No. 766,290 and Canadian Patent 562,672 and those obtainable'by condensing terephthalic acid and dimethyl terephthalate with propylene glycol, dimethylene glycol, tetramethylene glycol or cyclohexane-l ,4-dimethanol(hexahydro-p-xylene alcohol). The films of Bauer et al., U.S. Pat. No. 3,059,543 may also be used. The above polyester films are'particularly suitable because of their dimensional stability; The emulsions are generally coated on the supports to.

give a silicone nitrate coating weight equivalent it?" the group consisting of metalloboranes, metallothiaboranes and metallocarboranes, said borane having three or eight to 1 l boron atoms and containing in its structure at least one metal selected from the group consisting of platinum, nickel, cobalt, rhenium, iron and silver. I

2. An emulsion according to claim 1 having a pH below about 9.0.

3. An emulsion according to claim 1 wherein the amount ranges from l0- to 10 mole per 1.5 moles of silver.

4. An emulsion according to claim 3 containing a salt of rhodium or iridium.

5. An emulsion according to claim 3 wherein the silver halide is silver chloride.

6. An emulsion according to claim 3 wherein the silver halide is silver chlorobromide. v

7. An emulsion according to claim 3 wherein said colloid is gelatin.

8. A direct-positive photographic element comprising a sheet support bearing a layer of a silver halide emulsion as defined in claim 3.

9. An element according to claim 8, wherein the silver halide is silver chloride.

10. An element according to claim 8 wherein the silver halide is silver chlorobromide.

11. An element according to claim 8 containing a salt 

2. An emulsion according to claim 1 having a pH below about 9.0.
 3. An emulsion according to claim 1 wherein the amount ranges from 10 8 to 10 4 mole per 1.5 moles of silver.
 4. An emulsion according to claim 3 containing a salt of rhodium or iridium.
 5. An emulsion according to claim 3 wherein the silver halide is silver chloride.
 6. An emulsion according to claim 3 wherein the silver halide is silver chlorobromide.
 7. An emulsion according to claim 3 wherein said colloid is gelatin.
 8. A direct-positive photographic element comprising a sheet support bearing a layer of a silver halide emulsion as defined in claim
 3. 9. An element according to claim 8, wherein the silver halide is silver chloride.
 10. An element according to claim 8 wherein the silver halide is silver chlorobromide.
 11. An element according to claim 8 containing a salt of rhodium or iridium. 